The International Atomic Energy Agency (IAEA) reported that Iran has expanded its Natanz nuclear site.
The IAEA report said that the country has begun installing advanced centrifuges while simultaneously reducing the stockpiling of uranium.
The nuclear watchdog releases a report on Iran's nuclear progress every quarter.
Iran had informed the IAEA recently that it was installing so-called IR2m centrifuges, which enrich uranium two to three times faster than older ones.
BBC reported that Iran's stockpile of 20 percent uranium enrichment reached 368 lbs. this month.
Another few hundred pounds could allow Iran to build one bomb, said RT.
Tehran has maintained that it is enriching uranium for peaceful purposes while Western powers believe that it is moving towards nuclear weapons.
US officials said that the actions are "another provocative step" by Iran.
"The installation of new advanced centrifuges would be a further escalation, and a continuing violation of Iran's obligations under the relevant UN Security Council resolutions and IAEA board resolutions," said State Department spokseman Victoria Nuland, reported BBC.
Talks between Iran and the IAEA failed recently to produce results.
The IAEA wants more access to nuclear sites, scientists and documents.
Iran and the five permanent members the UN Security Council, and Germany will begin nuclear talks in Kazakhstan on February 26.